This invention relates to products of dough-like consistency exhibiting reduced water activity containing derived protein-containing compositions and particularly byproducts obtained from concentrating whey protein by means of ultrafiltration or gel filtration.
It is well known that foods can be preserved by drying. It is also known that some foods having a moisture level between fresh and dried are stable and do not contain sufficient moisture to support bacteriological growth, i.e., cheese. Because of the recognition of this factor, a class of foods called "intermediate moisture foods" has arisen. One of the more important commercial examples of this class is semi-moist pet foods.
In order to determine if the semi-moist food will be stable, it is necessary to determine the water activity, a.sub.w, of the product. Water activity is defined as the ratio of the materials' water vapor pressure to the vapor pressure of pure water at saturation in air at the temperature of the material.
This can be represented mathematically by the formula: ##EQU1## wherein the water activity is a.sub.w, P.sub.s is the vapor pressure of water vapor in the food, P.sub.o is the vapor pressure of pure water at the same temperature, N.sub.w is moles of water and N.sub.s is moles of solute (Commercial Development of Intermediate Moisture and Food, M. Kaplow, Food Technology, Volume 28, page 889, August 1970).
One method of determining water activity involves humidifying samples in desiccators at 37.degree. C. to the desired water activity by using reference saturated salt solutions. The procedure involves placing the sample uncovered in the desiccator and leaving the sample in the desiccator to equilibrate. Moisture isotherms are prepared by determining gravimetrically the weight increase of the samples. Illustrative reference saturated salt solutions are as follows:
TABLE I ______________________________________ Salt a.sub.w at 25.degree. C. a.sub.w at 30.degree. C. ______________________________________ Magnesium Chloride MgCl.sub.2 0.328 0.324 Potassium Carbonate K.sub.2 CO.sub.3 0.432 0.432 Magnesium Nitrate MgNO.sub.3 0.529 0.514 Sodium Bromide NaBr 0.576 0.560 Cobalt Chloride CoCl.sub.2 0.649 0.618 Strontium Chloride SrCl.sub.2 0.709 0.691 Sodium Nitrate NaNO.sub.3 0.743 0.731 Sodium Chloride NaCl 0.753 0.751 Potassium Bromide KBr 0.809 0.803 Ammonium Sulfate (NO.sub.4).sub.2 SO.sub.4 0.810 0.806 Potassium Chloride KCl 0.843 0.836 Strontium Nitrate Sr(NO.sub.3).sub.2 0.851 Barium Chloride BaCl.sub.2 0.902 Potassium Nitrate KNO.sub.3 0.936 0.923 Potassium Sulfate K.sub.2 SO.sub.4 0.973 0.970 ______________________________________
It has been reported that typical intermediate moisture foods have water contents of from 15% to 30% on a dry solids basis and water activities lower than 0.85. Fresh foods generally have more than 60% moisture and an a.sub.w of greater than 0.90. Dry foods have a moisture content of less than 15% and an a.sub.w of less than 0.20.
Three problems are connected with the stability of intermediate moisture foods, i.e., microorganisms, browning and lipid oxidation. Depressing the water activity has an inhibiting effect on the growth of microorganisms and, apparently, an antioxidant effect on lipid oxidation.
Stille (1948) has suggested an a.sub.w of 0.75 as an overall limit for most foods stored in cool environments. Mossel and Ingram (1955) have suggested an a.sub.w of 0.70 for long term storage in tropical climates. Mossel and Sand (1968) suggest inhibition of all microorganisms occurs only below a.sub.w of 0.60. It is noted that these are guidelines. Moisture isotherms shift with temperatures such that storage at a higher temperature with the same moisture content gives a higher a.sub.w than storage of the same product at lower temperature.
Water activity below which microorganism growth if inhibited is illustrated by the following though these amounts can vary:
TABLE II ______________________________________ Organism Water Activity a.sub.w ______________________________________ Bacteria 0.91 Yeasts 0.88 Molds 0.80 ______________________________________ (NASA CONTRACTOR REPORT, NASA CR 114,861, June 1972, Table 1, page 77).
Because the stability is dependent on available moisture and not total moisture, much research has been done in the area of humectants. In descending order of effectiveness as humectants are sodium chloride, potassium chloride, propylene glycol, glycerol 1-3-butylene glycol, sorbitol, fructose, polyethylene glycol 400, glucose, sucrose, 42 D.E. corn syrup solids and lactose. It has also been suggested that dried whey, delactosed whey and whey protein concentrate may find utility as humectants. While sodium and potassium chloride are 2-2.5 times more effective than propylene glycol, they have not been used for humectants due to flavor problems. While propylene glycol and glycerol are highly effective as humectants, they are detectable by pets who dislike the taste. Compositions which provide effective water activity and good taste are needed to overcome the problems incurred in using prior art materials in preparing intermediate moisture foods.
It is also known that, because of the increasing requirement for protein sources throughout the world, various processes have been recently developed to extract protein from whey. Particular reference is made to the Dienst Attebery patent, U.S. Pat. No. Re. 27,806, which discloses a method of separating protein from cheese whey by means of molecular sieve resin, more commonly known as gel filtration. Also in active use is the technique of ultrafiltration to separate and concentrate the protein from the whey. The development of the separation techniques has also raised further processing problems. The byproducts from these processes are not easily adaptable to present known techniques of material handling.
In the processing of cheese whey by molecular sieve resin, a low molecular weight fraction (about 5-10% solids) is obtained which has a solids composition of mainly lactose and minerals with residual protein. The solids in this low molecular weight fraction can be described more particularly by the following typical chemical analysis.
______________________________________ Lactose, % 40-50 Minerals, % 25-35 Protein (N .times. 6.38), % 15-20 Lactic Acid, % 7-10 Citric Acid, % 3-6 Fat, % less than 1 Moisture less than 5 pH 6.6-7.2 ______________________________________
Similarly, the use of ultrafiltration provides a permeate which is high in minerals and lactose. The solids in the permeate can be described more particularly by the following typical chemical analysis.
______________________________________ Lactose, % 70-80 Minerals, % 10-15 Protein, (N .times. 6.38), % 4-8 Fat, % less than 1 Moisture less than 5 pH 6-7 ______________________________________
After removing the lactose by normal lactose crystallization procedures, the now delactosed permeate contains from about 40% to about 45% lactose, from about 25% to about 35% ash and from about 8% to about 12% protein (TKN.times.6.38). However, the total Kjeldahl nitrogen (TKN) is a measure of all the nitrogen in the system (protein as well as non-protein nitrogen), and this is an approximation of the total protein present. While the delactosed permeate is indicated to have 8-12% protein (TKN.times.6.38), more than 60% of this protein is based on non-protein nitrogen, i.e., derived protein and amino acids. Derived protein is defined as a decomposition product of proteins that is intermediate in complexity of structure between proteins and amino acids (Hackh's Chemical Dictionary, 3rd Edition).
Two primary problems have been associated with the low molecular weight fraction and the permeate. First of all, conventional drying techniques cannot be utilized due to undesirable particle adherence to the walls. The second problem associated with these products is the undesirably high level of hygroscopicity exhibited by these products. The products, particularly delactosed permeate, rapidly pick up moisture from the air. Also, the undesirable level of hygroscopicity tends to detract from the potential use of this product in food applications. Once the package is opened, the dried particles immediately absorb moisture and cake.
It is also known to utilize the permeate and delactosed permeate in the formation of an egg albumen extender. In assignee's copending application Ser. No. 970,688, now U.S. Pat. No. 4,238,519, issued Dec. 9, 1980, the disclosure of which is incorporated herein by reference, there are disclosed egg albumen extenders comprising at least 65% by weight on a dry solids basis of a derived protein-containing composition from plant or animal sources wherein said derived protein-containing composition has a molecular weight of less than 20,000, a total Kjeldahl nitrogen content of from about 0.45% to about 2.1% of which at least 60% of the nitrogen is non-protein nitrogen, and from 0% to about 30% of a whipping aid, in combination with a member selected from the group consisting of gelatin, gelatin and a water soluble polyphosphate, a gum, and mixtures thereof. It has been found that these products are also difficult to dry when prepared from the liquid byproduct solution. Dry blending cannot be accomplished due to the difficulties in drying the byproduct solution before blending.
An improved process for drying a mineral containing aqueous protein solution is disclosed in U.S. Pat. No. 3,840,996. In this patent, the low molecular weight byproduct fraction from the gel filtration of the whey is admixed with inorganic drying agents selected from the group consisting of tricalcium phosphate, dicalcium phosphate, kaolin, diatomaceous earth, silica ggel, calcium silicate hydrate, or mixtures thereof and spray dried. This product is useful in flavor-enhancing various foods.
In assignee's copending application Ser. No. 6,817, it is disclosed that mineral containing deproteinized whey byproduct solutions can be more effectively dried by mixing from about 5% to about 50% casein or alkali metal caseinates with the solution and codrying the solution. However, the high cost of casein and caseinates make this process economically unattractive.
It has now been found that dough-like products exhibiting reduced water activity and good flavor for preparing intermediate moisture foods can be obtained containing derived protein-containing compositions and particularly deproteinized mineral-containing whey byproducts of whey protein concentrate.